1. Field of the Invention
This invention relates to a new composition of matter comprising copolymers of oxiranes, preferably polyoxirane compounds and aromatic polyimides. More specifically, it relates to such compositions in which the polyimides are amine-terminated polymers. Still more specifically, it relates to such oxirane-polyimide copolymers having improved tractability as compared to polyimide polymers per se.
2. State of the Prior Art
Polyimide resins as prepared from aromatic dianhydrides and aromatic diamines are known to have the desired property of high heat resistance and high solvent resistance. However because of these very same properties, they are untractable and therefore very difficult and expensive to work into desired shapes and forms.
On the other hand, while polymers derived from oxirane compounds, such as epoxy phenolics, i.e., resins from diglycidyl bis-phenol-A, etc., may be cured at reasonably low temperatures, the thermal stability of such polymers is much less than desired. To facilitate economical use of the polyimide resins, it would be desirable to prepare low molecular weight polymers, or oligomers, which may be copolymerized at relatively low temperatures to insoluble, infusible higher molecular weight polymers with little or no by-product formation and with thermal stabilities improved over epoxy phenolics. Moreover, it would also be desirable to convert the less expensive polymers derived from oxirane compounds to compositions having improved heat stability.
Several recent patents, such as U.S. Pat. Nos. 3,897,395 and 4,026,904 show the extension of aromatic polyimides by the coupling of terminal groups. In U.S. Pat. No. 3,897,395, the coupling groups are primarily unsaturated groups such as vinyl, propargyl, etc., and in U.S. Pat. No. 4,026,904, vinyl terminated polyimides are peroxidized to give epoxy-terminal groups. However, in neither of these patents has there been found any reference or disclosure to the copolymerization of oxirane compounds, particularly polyoxirane compounds with amine-terminated aromatic polyimides.
In the prosecution of the parent application, Chalmers et al, U.S. Pat. No. 3,416,994 was cited. However, as shown hereinafter in Example XVI, the polymer used by patentees with epoxy compositions is one having predominantly --COOH and --CONH-- groups along the polymer chain. Therefore because of the preponderance of these, the epoxy groups will react with these instead of the terminal amine groups. Moreover because of the conditions used in producing the ultimate polyimide structure, this will be crosslinked and insoluble and its terminal amine groups inaccessible for epoxy reaction.